(1) Field of the Invention
This invention relates to a cutting head construction for cutter suction dredgers used for the underwater cutting of rock, earth, ores, clay and sand, hereinafter referred to generically as soil. The cutting head construction is of generally conical shape and comprises a number of helical cutting arms fixed at their one ends to a hub and at their other ends to a base ring. A plurality of cutting teeth are mounted on these cutting arms.
(2) Description of the Prior Art
In the operation of a cutter suction dredger the cutting head is rotated in contact with the soil while simultaneously being swung along successive, generally arcuate paths.
This invention relates in particular to the positioning of the teeth on the arms in positions in which the tooth tips intersect a plane extending through the axis of rotation of the cutting head.
In this respect there are two commonly used arrangements, namely:
(a) The tooth tip positions on all cutting arms coincide; this is called a non-staggered arrangement, and PA1 (b) The tooth tip positions on each cutting arm are in between those on the adjacent cutting arms; this arrangement is generally called a staggered arrangement.
The arrangement of tooth tip positions defines the cutting process of a tooth in soil and thus the size and shape of the piece of soil removed per tooth, which is also influenced by the rotational speed of the cutterhead and the swing velocity of the cutter suction dredger.
Due to the generally conical shape of the cutterhead neither the non-staggered nor the staggered arrangement produces a well-balanced cutting pattern in which all teeth cut off substantially symmetrical pieces of soil with substantially normal cutting forces per tooth which are as small as possible so that lateral force action on the tooth is minimized. Normal force or normal load as used herein means the force perpendicular to a plane which: (1) extends through the cutter head rotational exis, (2) extends perpendicular to the cutter head rotational axis, (3) extends through the tooth-tip, and (4) extends parallel to the cutter head base ring.